Heat treatment apparatus and heat treatment method for measuring particle concentration

ABSTRACT

A heat treatment apparatus includes a chamber for receiving a substrate therein, and a measurement part for measuring an air particle concentration in a processing space provided in the chamber. An air particle concentration in the processing space provided in the chamber is measured by the measurement part. The air particle concentration is correlated with the number of particles attached to a substrate received in the chamber. Accordingly, by conducting a particle test after the air particle concentration in the processing space is lowered to an air particle concentration corresponding to the number of particles existing on the substrate which can pass the particle test, the number of times the particle test should be conducted after maintenance of the heat treatment apparatus can be reduced.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/895,540, filed May 16, 2013, which claims the benefit of JapanesePatent Application Nos. 2013-063384, filed Mar. 26, 2013, and2012-117475, filed May 23, 2012, both incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a heat treatment technology for heatinga semiconductor wafer, a glass substrate, or the like, (hereinafter,simply referred to as “substrate”) that is placed in a process chamber.

2. Description of the Background Art

As well known, a semiconductor component or the like is manufacturedthrough a large number of process steps, and various manufacturingapparatuses corresponding to the respective process steps are used. Manyof the apparatuses are each provided with a cleaning mechanism thereinbecause the manufacture of the semiconductor component or the like,which is becoming finer and finer, requires an ultraclean atmosphere.For example, Japanese Patent Application Laid-Open No. 7-321046 (1995)discloses a technique that causes an ozone gas to flow under ultravioletirradiation, to thereby remove an organic substance existing on asubstrate. Japanese Patent Application Laid-Open No. 9-17705 (1997)discloses a technique in which an unnecessary film attached to a surfaceof an inner wall of a process chamber or to a surface of a structureinside the process chamber is cleaned away at about 200° C. with asupply of a ClF₃ gas thereto. Japanese Patent Application Laid-Open No.7-230954 (1995) discloses a cleaning technique in which, in a plasmaprocessing apparatus, a residual material attached to a surface of astructural component inside a chamber (process chamber) is heated andthereby decomposed and removed.

Steps for manufacturing a semiconductor component or the like include anion implantation step of implanting ions of boron, arsenic, or the like,into a silicon wafer (substrate). For the purpose of activating the ionsimplanted in the substrate, a heat treatment is performed. The heattreatment for activating ions is implemented by heating (annealing) thesubstrate to a temperature of, for example, about 1000° C. to 1100° C.

In a heat treatment apparatus that performs such a heat treatment, afault such as a defect or cracking may occur in the substrate due to theheat treatment. For example, in flash annealing that is a heat treatmentusing flash lamps, the substrate may be broken and a shape fault such asa defect or cracking may occur in the substrate because of an impactcaused by instantaneous radiation of light with an enormous amount ofenergy at a time of flash heating or because the substrate is moved upby a quartz-made arm having a temperature lower than the heat-treatedsubstrate.

A breakage of the substrate causes a large amount of particles in theprocess chamber due to broken pieces of the substrate itself, damage toperipheral structures, and the like. When a breakage of the substrateoccurs, needless to say, the process chamber is opened and maintenanceis carried out, for the collection of the broken pieces and the like.However, it is very difficult to completely remove the caused particles.Additionally, opening the process chamber undesirably allows particlesexisting outside to be newly taken into the process chamber. When theflash heating treatment is performed under a state where particlesremain in the process chamber, the particles are attached to thesubstrate and cause a process fault.

Conventionally, therefore, a method has been adopted in which, after theprocess chamber is opened and the maintenance is carried out, the flashheating is performed on a dummy wafer to thereby attach particles to thedummy wafer, and the particles are removed. In more detail, in thismethod, a particle removal process and a comparison and examinationprocess (“particle test”) are repeated until a measurement result of theparticle test becomes equal to or less than a predetermined allowablevalue. In the particle removal process, particles are attached to thedummy wafer by means of the flash heating. In the comparison andexamination process, the dummy wafer is taken out from the processchamber and transported into a measuring apparatus that is separatelyprovided and configured to measure the number of particles attached ontothe wafer. Then, the number of particles attached to the dummy wafer ismeasured, and the measurement result is compared and examined againstthe predetermined allowable value. However, to reach a state where themeasurement result of the particle test is equal to or less than thepredetermined allowable value, normally, it is necessary to repeat theparticle removal process and the particle test a considerable number oftimes. Moreover, it is normally not easy to perform the particle testin, for example, a user's manufacturing plant in which the heattreatment apparatus is installed. Accordingly, a cleaning process forcleaning the inside of the process chamber after the maintenancerequires a considerable number of dummy wafers and a process time, whichcauses a problem of a large cost increase.

Therefore, in a heat treatment apparatus disclosed in U.S. Pat. No.7,068,926, a method is adopted in which a particle removal process forremoving particles existing in a process chamber is implemented byrepeating emission of flashes of light in an empty process chamberhaving no wafer, to thereby cause particles to scatter within theprocess chamber, and then exhausting the process chamber. In thismethod, when the number of times of emission of flashes of light, whichis repeated at predetermined time intervals, reaches a predeterminedvalue, it is determined that the number of particles in the processchamber becomes equal to or less than an allowable limit. Thus, theemission of flashes of light process is stopped. Then, similarly to theconventional method, the particle test is performed by actually using adummy wafer. Based on a result of the particle test, whether or not thecleaning process for cleaning the inside of the process chamber iscompleted is determined.

However, in the apparatus disclosed in U.S. Pat. No. 7,068,926, it isdetermined that the number of particles existing in the process chamberbecomes equal to or less than the allowable limit, based on the factthat the number of times the flash heating is performed in the emptyprocess chamber reaches a predetermined value. Accordingly, in a casewhere the number of particles in the process chamber is larger thanassumed, the particle test using the dummy wafer is performed under astate where the inside of the process chamber has not been sufficientlycleaned. As a result, the particle removal process using the flashheating and the particle test using the dummy wafer have to be performedagain. In this manner, the apparatus disclosed in U.S. Pat. No.7,068,926 still involves a problem that repetition of the particle testmay result in the need for a considerable number of dummy wafers and aprocess time.

Moreover, conventionally, a situation sometimes occurs in which, in thecourse of continuously performing the heat treatment on a lot includinga plurality of substrates, the degree of cleanliness in the processchamber rapidly deteriorates. A conceivable cause of the deteriorationin the degree of cleanliness is, for example, the bringing-in ofparticles by the substrates or a trouble occurring in a gas supply andexhaust system for supplying and exhausting a gas to and out of theprocess chamber. Here, in the conventional heat treatment apparatus,even though the degree of cleanliness in the process chamberdeteriorates during the process, detection thereof is difficult. Thus,the deterioration cannot be promptly responded to, and there is a fearthat a large number of mis-processed substrates may be produced.Additionally, in a case where the degree of cleanliness in the processchamber deteriorates during the process, it is necessary to open theprocess chamber and carry out the maintenance. This causes a problem ofa prolonged downtime.

SUMMARY OF THE INVENTION

The present invention is directed to a heat treatment apparatus forheating a substrate.

In an aspect of the present invention, a heat treatment apparatusincludes: a process chamber for receiving a substrate therein; and ameasurement part for measuring an air particle concentration in aprocessing space provided in said process chamber.

The air particle concentration is correlated with the number ofparticles attached to a substrate received in the process chamber.Accordingly, by conducting a particle test after the air particleconcentration in the processing space is lowered to an air particleconcentration corresponding to the number of particles existing on thesubstrate which can pass the particle test, the number of times theparticle test should be conducted after maintenance of the heattreatment apparatus can be reduced.

The present invention is also directed to a particle measurement methodfor measuring the number of particles attached to a substrate receivedin a process chamber of a heat treatment apparatus.

In an aspect of the present invention, a particle measurement methodincludes the steps of: (a) obtaining correlation information thatindicates the correlation between an air particle concentration in aprocessing space provided in the process chamber and the number ofparticles attached to a substrate received in the process chamber; (b)measuring an air particle concentration in the processing space; and (c)based on the air particle concentration obtained as a result of themeasurement in the step (b) and the correlation information, calculatingthe number of particles that will be attached to a substrate intended tobe received in the process chamber.

By conducting a particle test after the air particle concentration inthe processing space is lowered to an air particle concentrationcorresponding to the number of particles existing on the substrate whichcan pass the particle test, the number of times the particle test shouldbe conducted after maintenance of the heat treatment apparatus can bereduced.

The present invention is further directed to a heat treatment method forheating a substrate.

In an aspect of the present invention, a heat treatment method includesthe steps of: (a) causing a substrate to be received in a processchamber; (b) heating the substrate in the process chamber; (c) measuringan air particle concentration in a processing space provided in theprocess chamber during the step (b); and (d) in a case where the airparticle concentration obtained as a result of the measurement in thestep (c) exceeds a predetermined threshold value, removing particlesexisting in the process chamber.

When the air particle concentration obtained as a result of themeasurement exceeds the predetermined threshold value, particlesexisting in the process chamber are removed. Accordingly, even when theparticle concentration in the process chamber increases during theprocess of the substrate, the number of particles can be promptlyreduced.

Preferably, in an aspect of the present invention, in a case where theair particle concentration obtained as a result of the measurement inthe step (c) exceeds a first threshold value, in the step (d), particlesexisting in the process chamber are removed with a maximum flow rate ofthe supply and exhaust to and out of the process chamber.

Preferably, in an aspect of the present invention, in a case where theair particle concentration obtained as a result of the measurement inthe step (c) exceeds a second threshold value that is greater than thefirst threshold value, in the step (d), particles existing in theprocess chamber are removed while a substrate is being imaginarilytransported.

Preferably, in an aspect of the present invention, in a case where theair particle concentration obtained as a result of the measurement inthe step (c) exceeds a third threshold value that is greater than thesecond threshold value, in the step (d), the process chamber is openedand maintenance is carried out.

Therefore, an object of the present invention is to reduce the number oftimes the particle test should be conducted after the maintenance.

Another object of the present invention is to promptly reduce the numberof particles even when the particle concentration in the process chamberincreases during the process of the substrate.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a side cross-sectional view showing a configuration of a heattreatment apparatus according to a first preferred embodiment;

FIG. 2 is a side cross-sectional view showing the configuration of theheat treatment apparatus according to the first preferred embodiment;

FIG. 3 is a block diagram showing a configuration of a controller of theheat treatment apparatus shown in FIG. 1;

FIG. 4 shows an example of the correlation between an air particleconcentration and the number of particles existing on a substrate;

FIG. 5 is a flowchart of a process in the heat treatment apparatusaccording to the first preferred embodiment;

FIG. 6 is a flowchart of the process in the heat treatment apparatusaccording to the first preferred embodiment;

FIG. 7 is a flowchart of a process in the heat treatment apparatusaccording to the first preferred embodiment;

FIG. 8 is a flowchart of a process in a heat treatment apparatusaccording to a second preferred embodiment;

FIG. 9 is a flowchart showing procedures taken when the air particleconcentration exceeds a level 3;

FIG. 10 is a flowchart showing procedures taken when the air particleconcentration exceeds a level 2;

FIG. 11 is a flowchart showing procedures taken when the air particleconcentration exceeds a level 1; and

FIG. 12 shows the correlation between the increment of the number ofparticles on a semiconductor wafer and the air particle concentrationbefore and after a process.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a preferred embodiment of the present invention will bedescribed with reference to the accompanying drawings. Note that thesame reference numerals in the drawings denote components that have thesame configurations and functions, and a repetitive description thereofwill be omitted. Also note that the drawings are merely schematicrepresentations and do not necessarily reflect the exact size,positional relationship, and the like, of the parts shown in thedrawings.

First Preferred Embodiment

<1. Configuration of Heat Treatment Apparatus>

FIGS. 1 and 2 are side cross-sectional views showing a configuration ofa heat treatment apparatus according to the present invention. The heattreatment apparatus is an apparatus for heat-treating a substrate suchas a circular semiconductor wafer by using a light flash (flashes oflight) from xenon flash lamps.

The heat treatment apparatus includes a chamber 65. The chamber 65includes a light-transmittable plate 61, a bottom plate 62, and a pairof side plates 63 and 64, and receives a semiconductor wafer W thereinto heat-treat the semiconductor wafer W. The light-transmittable plate61 constituting an upper portion of the chamber 65 is made of, forexample, a material transmissive to infrared light, such as quartz. Thelight-transmittable plate 61 functions as a chamber window for allowinglight emitted from a light source 5 to pass therethrough into thechamber 65. The bottom plate 62 constituting the chamber 65 is providedwith upright support pins 70 that extend through a susceptor 73 and aheating plate 74, which will be described later, and support the lowersurface of the semiconductor wafer W.

The side plate 64 constituting the chamber 65 is provided with anopening 66 for the transport of the semiconductor wafer W therethroughinto and out of the chamber 65. The opening 66 is openable and closableby a gate valve 68 pivoting about an axis 67. With the opening 66 open,the semiconductor wafer W is transported into the chamber 65 by atransport robot (not shown). During a heat treatment of thesemiconductor wafer W in the chamber 65, the opening 66 is closed by thegate valve 68.

The chamber 65 is provided under the light source 5. The light source 5includes a plurality of (in this preferred embodiment, thirty) xenonflash lamps 69 (hereinafter, also referred to simply as “flash lamps69”), and a reflector 71. The plurality of flash lamps 69, each of whichis a rod-like lamp having an elongated cylindrical shape, are arrangedin parallel with one another such that a lengthwise direction thereofextends horizontally. The reflector 71 is provided over the plurality offlash lamps 69 to cover all of the flash lamps 69.

Each of the xenon flash lamps 69 includes a glass tube and a triggerelectrode. The glass tube contains xenon gas sealed therein, andincludes positive and negative electrodes that are provided on oppositeends of the glass tube and that are connected to a capacitor. Thetrigger electrode is wound around the glass tube. Since the xenon gas iselectrically insulative, no current flows in the glass tube in a normalstate. However, if a high voltage is applied to the trigger electrode toproduce an electrical breakdown, electricity stored in the capacitorflows momentarily in the glass tube, and excitation of xenon atoms ormolecules occurring at this time causes light emission. The xenon flashlamps 69 have the property of being capable of emitting much intenserlight than a light source that continuously stays lit, becausepreviously stored electrostatic energy is converted into an ultrashortlight pulse ranging from 0.1 millisecond to 10 milliseconds.

A light diffusion plate 72 is arranged between the light source 5 andthe light-transmittable plate 61. The light diffusion plate 72 usedherein is made of quartz glass, which is an infrared-transmissivematerial, with a surface thereof having been subjected to a lightdiffusion process.

A part of the light emitted from the flash lamps 69 directly passesthrough the light diffusion plate 72 and the light-transmittable plate61 into the chamber 65. A different part of the light emitted from theflash lamps 69 is once reflected from the reflector 71 and then passesthrough the light diffusion plate 72 and the light-transmittable plate61 into the chamber 65.

The heating plate 74 and the susceptor 73 are provided in the chamber65. The susceptor 73 is bonded to the upper surface of the heating plate74. Pins 75 for preventing the semiconductor wafer W from shifting outof place are mounted on a surface of the susceptor 73. In the chamber65, the semiconductor wafer W is held in a substantially horizontalattitude directly by the susceptor 73.

The heating plate 74 is provided for preheating (or assist-heating) thesemiconductor wafer W. The heating plate 74 is made of aluminum nitride,and is structured to incorporate therein a heater and a sensor forcontrolling the heater. The susceptor 73, on the other hand, is providedfor positioning and holding the semiconductor wafer W and for diffusingthermal energy given from the heating plate 74 to thereby uniformlypreheat the semiconductor wafer W. For the susceptor 73, a materialhaving a relatively low thermal conductivity, such as aluminum nitrideor quartz, is adopted.

The susceptor 73 and the heating plate 74 are driven by a motor 40 tovertically move between a wafer transport position in which thesemiconductor wafer W is transported into and out of the chamber 65 asshown in FIG. 1 and a wafer heat treatment position in which thesemiconductor wafer W is heat-treated as shown in FIG. 2.

Specifically, the heating plate 74 is coupled to a movable plate 42 by atubular element 41. The movable plate 42 is guided by a guide member 43suspended from the bottom plate 62 of the chamber 65 such that themovable plate 42 is vertically movable. A fixed plate 44 is fixed to thelower end of the guide member 43, and the motor 40 for rotatably drivinga ball screw 45 is provided in a central portion of the fixed plate 44.The ball screw 45 is in threaded engagement with a nut 48 coupled to themovable plate 42 by coupling members 46 and 47. With this arrangement,the susceptor 73 and the heating plate 74 are driven by the motor 40 andthereby can be moved vertically between the wafer transport position inwhich the semiconductor wafer W is transported into and out of thechamber 65 as shown in FIG. 1 and the wafer heat treatment position inwhich the semiconductor wafer W is heat-treated as shown in FIG. 2.

The wafer transport position shown in FIG. 1 corresponds to the positionof the susceptor 73 and the heating plate 74 being lowered so that thesemiconductor wafer W transported through the opening 66 into thechamber 65 is placed onto the support pins 70 by means of the transportrobot (not shown) or so that the semiconductor wafer W placed on thesupport pins 70 is transported through the opening 66 out of the chamber65 by means of the transport robot (not shown). Specifically, thesusceptor 73 and the heating plate 74 which are vertically movable areprovided with through holes which enable the support pins 70 fixedupright on the bottom plate 62 to pass therethrough relative to thesusceptor 73 and the heating plate 74. When the susceptor 73 and theheating plate 74 move downward to the wafer transport position, theupper ends of the support pins 70 protrude out of the upper surface ofthe susceptor 73 and a state where the semiconductor wafer W isreceivable thereon is created, as shown in FIG. 1.

The wafer heat treatment position shown in FIG. 2, on the other hand,corresponds to the position of the susceptor 73 and the heating plate 74being raised above the upper ends of the support pins 70 for the heattreatment of the semiconductor wafer W. When the susceptor 73 and theheating plate 74 move upward to the wafer heat treatment position, theupper ends of the support pins 70 are below the upper surface of thesusceptor 73 as shown in FIG. 2, and the semiconductor wafer W placed onthe support pins 70 is received by the susceptor 73. Thus, the motor 40vertically moves the susceptor 73 and the heating plate 74 relative tothe support pins 70 between the wafer transport position shown in FIG. 1and the wafer heat treatment position shown in FIG. 2.

In the course of the downward movement of the susceptor 73 and theheating plate 74 from the wafer heat treatment position shown in FIG. 2to the wafer transport position shown in FIG. 1, the semiconductor waferW supported by the susceptor 73 is transferred to the support pins 70.On the other hand, in the course of the upward movement of the susceptor73 and the heating plate 74 from the wafer transport position shown inFIG. 1 to the wafer heat treatment position shown in FIG. 2, thesemiconductor wafer W placed on the support pins 70 is received by thesusceptor 73, is lifted with the lower surface thereof supported by theupper surface of the susceptor 73, and is held in a horizontal attitudein proximity to the light-transmittable plate 61 in the chamber 65.

When the susceptor 73 and the heating plate 74 that support thesemiconductor wafer W are raised to the wafer heat treatment position,the light-transmittable plate 61 is situated between the light source 5and the semiconductor wafer W held by the susceptor 73 and heating plate74. A distance between the susceptor 73 and the light source 5 at thistime is adjustable to any value by controlling the amount of rotation ofthe motor 40.

An expandable/contractible bellows 77 surrounding the tubular element 41for maintaining the chamber 65 hermetically sealed is provided betweenthe bottom plate 62 of the chamber 65 and the movable plate 42. Thebellows 77 contacts when the susceptor 73 and the heating plate 74 areraised to the wafer heat treatment position, and expands when thesusceptor 73 and the heating plate 74 are lowered to the wafer transportposition. The bellows 77 cuts off communication between an atmosphereinside the chamber 65 and the external atmosphere.

The side plate 63 of the chamber 65 arranged on the side opposite to theopening 66 is formed with an inlet passage 78. The inlet passage 78 isconnected in communication with a gas source (not shown) through a gaspipe 82. An open-close valve 80 and a mass flow controller 89 areprovided in the gas pipe 82. Opening the open-close valve 80 can supplya gas that is required for a process, such as an inert nitrogen gas,into the chamber 65 through the distal end of the inlet passage 78. Theflow rate of the nitrogen gas supplied into the chamber 65 is controlledby the mass flow controller 89. At this time, the nitrogen gas isejected in a substantially horizontal direction. When the nitrogen gasis supplied through the inlet passage 78 while the susceptor 73 and theheating plate 74 are raised to the wafer heat treatment position, thenitrogen gas is supplied to a space between the heating plate 74 and thebottom plate 62, as shown in FIG. 2. In other words, the inert nitrogengas is supplied to a bottom portion of the chamber 65.

The opening 66 in the side plate 64, on the other hand, is provided withan outlet passage 79. The outlet passage 79 is connected incommunication with an exhaust element (not shown) through an exhaustpipe 83. An open-close valve 81 is provided in the exhaust pipe 83.Opening the open-close valve 81 causes the gas existing in the chamber65 to be discharged out of the outlet passage 79 through the opening 66.The exhaust pipe 83 is branched into to pipes, namely, a large-diameterpipe and a small-diameter pipe, and switching therebetween isimplemented by a switching valve (not shown). To exhaust the chamber 65with a high flow rate, the large-diameter pipe is selected. To exhaustthe chamber 65 with a low flow rate, the small-diameter pipe isselected.

The movable plate 42 is also formed with outlet passages 84. The distalends of the respective outlet passages 84 are in communication with thespace between the bellows 77 and the tubular element 41, and theproximal ends thereof are connected in communication with an exhaustelement (not shown) via exhaust pipes 86, respectively. Open-closevalves 85 are provided in the exhaust pipes 86, respectively. Openingthe open-close valves 85 causes the gas existing in the chamber 65 to bedischarged out of the outlet passages 84 through the space between thebellows 77 and the tubular element 41. In other words, the outletpassages 84 exhaust the gas in the interior space of the chamber 65through the bottom portion of the chamber 65, as shown in FIG. 2.

The side plate 63 is also formed with an inlet passage 91 extendingthrough the side plate 63. A tubular probe 92 having an inlet passagetherein is provided at the end of the inlet passage 91 on the chamber 65side, and a measurement part 50 is provided at the opposite end of theinlet passage 91. In the measurement part 50, a measurement chamberhaving a light emitting part 51, a light receiving part 52, and thelike, is formed. Via the inlet passage 91 and the probe 92, ameasurement space within the measurement chamber is connected incommunication with a processing space within the chamber 65. Themeasurement chamber of the measurement part 50 is formed with an outletpassage 93, and connected in communication with an exhaust system (notshown) via an exhaust pipe 94. The inside diameter of the outlet passage93 that exhausts the measurement part 50 is smaller than the insidediameters of the outlet passages 79 and 84 that exhaust the inside ofthe chamber 65. An open-close valve 95 is provided in the exhaust pipe94. Opening the open-close valve 95 causes the gas existing in theprocessing space of the chamber 65, to which pressure has been applieddue to the introduction of the nitrogen gas and the like, to beintroduced into the measurement chamber of the measurement part 50 witha substantially constant flow rate. The measurement space of themeasurement part 50 is tightly sealed by a portion of the side plate 63defining the edge of the opening of the inlet passage 91, in order toprevent a gas from entering the measurement chamber from places otherthan the processing space of the chamber 65. The probe 92 is providedfor the purpose of introducing, into the measurement part 50, a gasexisting in a place closer to an objective substrate to be processed.However, the usefulness of the present invention is not impaired eventhough a gas existing in any place in the processing space within thechamber 65 is introduced into the measurement chamber of the measurementpart 50. Therefore, the probe 92 is not an essential element.

The measurement part 50 is configured as an optical particle counter(OPC), to measure a particle concentration (“air particleconcentration”) in a gas existing within the chamber 65 which has beenintroduced into the measurement chamber of the measurement part 50. Themeasurement part 50 mainly includes the light emitting part 51, thelight receiving part 52, and a control computation part 53. The lightemitting part 51 is provided with a laser light source such as asemiconductor laser (not shown), a light-emitting optical system, andthe like. The light receiving part 52 is provided with a light-receivingoptical system (not shown), a processing circuit including a detectiondevice such as a photodiode, and the like. Laser light emitted from thelaser light source is condensed by the light-emitting optical system,and then emitted to a passage formed between the light emitting part 51and the light receiving part 52. In this passage, a gas introduced fromthe processing space within the chamber 65 into the measurement chamberof the measurement part 50 flows. When the laser light hits a particlecontained in the gas, scattering light is generated. The scatteringlight is, by the light-receiving optical system, imaged onto thedetection device of the processing circuit. Then, the processing circuitoutputs an electric pulse signal corresponding to each scattering lightthat has been incident on the detection device. The electric pulsesignal is supplied to the control computation part 53.

The control computation part 53 is implemented by, for example,execution of a predetermined program by a CPU. The control computationpart 53 controls operations of the light emitting part 51 and the lightreceiving part 52, and processes the pulse signal supplied from theprocessing circuit of the light receiving part 52. The crest value ofthis pulse signal is proportional to the amount of scattering light. Acorrelation based on the scattering theory is established between theamount of scattering light and a particle diameter of the particle. Theparticle diameter is calculated based on the crest value of the pulsesignal. The control computation part 53 calculates the particle diameterof the particle with respect to each of the electric pulse signalssupplied from the light receiving part 52, and, based on a predeterminedsize (particle diameter) that is preliminarily stored in a memory of thecontrol computation part 53, determines whether the calculated particlediameter is less than or not less than the predetermined size.

Based on a result of the determination, the control computation part 53counts the number of particles having particle diameters not less thanthe predetermined size which have been measured within a certain timeperiod, and the number of particles having particle diameters less thanthe predetermined size which have been counted within the certain timeperiod. Then, the control computation part 53 calculates a particleconcentration of the particles having particle diameters not less thanthe predetermined size and a particle concentration of the particleshaving particle diameters less than the predetermined size, based on theflow rate of a gas that passes per unit time through the passage betweenthe light emitting part 51 and the light receiving part 52, which ispreliminarily stored in the memory. Thereby, the control computationpart 53 measures two kinds of particle concentrations. Here, it may bealso possible that the control computation part 53 measures only one ofthe two kinds of particle concentrations in accordance with a controlgiven by the controller 10. The particle concentrations measured by thecontrol computation part 53 are supplied to the controller 10, and usedby the controller 10 for the conversion into the number of particlesexisting on the substrate, the determination of whether or not theparticle concentration is at a predetermined level, and the like.

In a case where the measurement part 50 is provided inside the outletpassage 79 or 84 that exhausts the interior of the chamber 65, there isa possibility that a particle concentration obtained as a result of themeasurement is higher than the actual particle concentration in thechamber 65, because of an influence of various remaining particles suchas metal particles that have been attached to the inside of the outletpassage at a time of processing the outlet passage 79 or 84. In thisrespect, the heat treatment apparatus according to this preferredembodiment has the outlet passage 93 that is dedicated for exhaust ofthe measurement part 50, so that the air particle concentration in thegas that has been introduced into the measurement chamber of themeasurement part 50 by the exhaust using the outlet passage 93 ismeasured. This can suppress a measurement error in measuring theparticle concentration, which may be normally caused because ofcontamination of the inside of the outlet passage 79 or 84.

The above-mentioned heat treatment apparatus further includes acontroller 10 for controlling mechanical components such as the motor40. FIG. 3 is a block diagram showing a configuration of the controller10. The controller 10 is similar to a typical computer in terms of ahardware configuration. Specifically, the controller 10 includes a CPU11 for performing various computation processes, a ROM 12 or read-onlymemory for storing a basic program therein, a RAM 13 orreadable/writable memory for storing various pieces of information, amagnetic disk 14 for storing control software and data therein, and abus line 19 connected to these components 11 to 14.

The bus line 19 is electrically connected to a display part 21 and aninput part 22. The display part 21 is configured with, for example, aliquid crystal display, and displays various pieces of information suchas processing results and recipe details. The input part 22 isconfigured with, for example, a keyboard and a mouse, and accepts theentry of a command, a parameter, and the like. An operator of the heattreatment apparatus can enter a command, a parameter, and the like,through the input part 22 while viewing the descriptions displayed onthe display part 21. The display part 21 and the input part 22 may beintegrated together into a touch panel device.

The bus line 19 is also electrically connected to the motor 40 of theheat treatment apparatus, the measurement part 50, a lamp power supplycircuit (not shown) for the flash lamps 69, and the open-close valves80, 81, 85, and 95. The bus line 19 is furthermore connected to theswitching valve of the exhaust pipe 83 and the mass flow controller 89of the gas pipe 82. The CPU 11 of the controller 10 executespredetermined software stored in the magnetic disk 14, and therebycontrols the turn-on timing of the flash lamps 69 and also controls themotor 40 to adjust the vertical position of the susceptor 73 and theheating plate 74. Additionally, the CPU 11 controls the open-closevalves, to thereby control the supply and exhaust of gases to and out ofthe chamber 65 and the measurement chamber of the measurement part 50.Moreover, the CPU 11 controls an operation of the measurement part 50,and, based on the particle concentration supplied from the measurementpart 50, calculates the number of particles attached to the substratereceived in the chamber 65.

FIG. 4 shows an example of the correlation between the air particleconcentration and the number of particles existing on the substratereceived in the chamber 65. As shown in FIG. 4, there is a correlationbetween the air particle concentration in the processing space of thechamber 65 and the number of particles attached to the substratereceived in the chamber 65. Normally, the number of particles existingon the substrate is proportional to the air particle concentration. Sucha correlation can be obtained in advance by means of experiments andsimulations. Correlation information indicating the correlation ispreliminarily identified and stored in the magnetic disk 14. Examples ofthe correlation information include a table indicating the correlation,a mathematical expression, and various other types of information. Basedon the correlation information and an air particle concentration almeasured by the measurement part 50, the CPU 11 calculates the number b1of particles that will be attached to the substrate intended to bereceived in the chamber 65. Instead, based on the correlationinformation, the CPU 11 can calculate an air particle concentration a1corresponding to a target number b1 of particles existing on thesubstrate. Furthermore, the CPU 11 also determines whether or not theair particle concentration obtained as a result of the measurement isequal to or less than a predetermined reference value stored in themagnetic disk 14. It may be also possible that the CPU 11 performs adetermination corresponding to this determination, by converting the airparticle concentration into the number of particles existing on thesubstrate.

The magnetic disk 14 stores not only the above-described correlationinformation but also various pieces of information used for an apparatusstart-up process that follows the maintenance. The various pieces ofinformation include the number of times and a time interval of emissionof flashes of light during the cleaning process, the predetermined size(particle diameter) serving as a criterion for determining the size ofthe particle diameter, a reference concentration for the particleconcentration, and the like. The above-mentioned predetermined size ofthe particle is supplied to, for example, the memory of the controlcomputation part 53 of the measurement part 50, and used by themeasurement part 50.

<2. Details of Process in Heat Treatment Apparatus>

Next, a process in the heat treatment apparatus according to the presentinvention will be described. FIGS. 5 to 7 are flowcharts showing aprocess in the heat treatment apparatus according to the presentinvention. FIGS. 5 and 6 show a process flow S100 of the apparatusstart-up process in a case where the maintenance is carried out in theheat treatment apparatus. FIG. 7 shows details of step S120 (FIG. 5)concerning the cleaning process (cleaning process) for cleaning theinterior of the chamber 65. The cleaning process shown in FIG. 7 isperformed by actuation of the mechanical components including the lamppower supply circuit in accordance with instructions given from thecontroller 10.

First, the maintenance of the heat treatment apparatus is carried out instep S110. The maintenance in step S110 may be carried out at regulartime intervals or at irregular time intervals, for example, whenever abreakage of the semiconductor wafer W occurs in the chamber 65. Ineither case, the maintenance is carried out while the light source 5 isremoved and the interior of the chamber 65 is open to the externalatmosphere. This causes external particles to enter the chamber 65during the maintenance. If the maintenance is due to a breakage of thesemiconductor wafer W, additional particles are generated from brokenpieces of the semiconductor wafer W.

After a predetermined maintenance process, the process proceeds to stepS120. In step S120, the light source 5 is mounted to the upper portionof the chamber 65 (to create the state shown in FIG. 1), and thecleaning process is performed to clean the interior of the chamber 65.In the cleaning process, the transport robot that transports a substrateinto the chamber 65 and the gate valve 68 are not driven. Then,particles existing in the chamber 65 and having particle diameters lessthan the predetermined size (particle diameter), for example, havingparticle diameters less than 0.8 um, are removed.

For performing the cleaning process, firstly, any objectivesemiconductor wafer W to be processed is prohibited from beingtransported into the chamber 65, and the susceptor 73 and the heatingplate 74 are moved upward to the wafer heat treatment position shown inFIG. 2 (in step S21). Thus, during the cleaning process, there is nosemiconductor wafer W in the chamber 65, and the susceptor 73 with nosemiconductor wafer W placed thereon is moved upward to the wafer heattreatment position. The heater in the heating plate 74 is turned ON tostart heating the heating plate 74.

After the susceptor 73 and the heating plate 74 move upward to the waferheat treatment position, a stream of nitrogen gas is produced in thechamber 65 (in step S22). Specifically, the open-close valves 80, 81 and85 are opened, to thereby produce a stream of nitrogen gas directed fromthe inlet passage 78 toward the outlet passages 79 and 84. Although theopen-close valve 81 may remain closed, the open-close valves 85 must beopened without fail. This produces a gas stream passing through a bottomportion of the chamber 65 and then exhausted out of the chamber 65, asindicated by the arrows in FIG. 2.

From the viewpoint of accurately determining whether or not there is anecessity to perform the cleaning again at a time when the cleaningprocess for cleaning the interior of the chamber 65 is completed, it ispreferable that a gas obtained at a time when the cleaning is completedso that the particle concentration in the processing space of thechamber 65 is made substantially uniform is introduced into themeasurement chamber of the measurement part 50. In a case where theopen-close valve 95 is opened, there is a risk that, when the turn-on ofthe flash lamps 69 is started, the particles may fly up from the bottomportion of the chamber 65 and the like, so that a gas having a locallyhigh particle concentration is introduced into the measurement part 50,which results in an inaccurate particle concentration being measured.Therefore, although the usefulness of the present invention is notimpaired even when the open-close valve 95 is not provided in theexhaust pipe 94, it is more preferable to provide the exhaust pipe 94and close the open-close valve 95 before the turn-on of the flash lamps69 is started.

Thereafter, the flash lamps 69 are turned on to emit flashes of lighttoward the interior of the chamber 65 (in step S23). A length of timeduring which the flash lamps 69 are ON ranges from about 0.1 millisecondto about 10 milliseconds. The flash lamps 69 emit extremely intenseflashes of light toward the interior of the chamber 65 becausepreviously stored electrostatic energy is converted into such anultrashort light pulse. The emission of the flashes of light from theflash lamps 69 heats the gas and the structural components in thechamber 65 so that instantaneous expansion and contraction of the gas inthe chamber 65 occurs, resulting in particles being raised andscattering in the chamber 65. Particularly in the bottom portion (theupper surface of the bottom plate 62) of the chamber 65, the particlesare likely to be deposited. However, as illustrated in this preferredembodiment, emitting the flashes of light under the state where theheating plate 74 is moved up to the wafer heat treatment position caneasily cause such particles deposited on the bottom portion to be raisedup.

The particles scattering in this manner is carried by the stream ofnitrogen gas and discharged to the outside of the chamber 65. Asdescribed above, the particles are likely to scatter particularly nearthe bottom portion of the chamber 65. However, in this preferredembodiment, the gas stream passing through the bottom portion of thechamber 65 and then exhausted out of the chamber 65 is produced.Therefore, the particles scattering near the bottom portion of thechamber 65 is efficiently discharged to the outside of the chamber 65.

The controller 10 determines whether or not a predetermined length oftime has elapsed since the turn-on of the flash lamps 69 (in step S24).That is, after the emission of the flashes of light is performed once,discharging of the particles is performed for the predetermined lengthof time. The stream of nitrogen gas passing through the bottom portionof the chamber 65 and then exhausted out of the chamber 65 continues tobe produced even during the lapse of the predetermined length of time.As the predetermined length of time, for example, one minute is set.

After the predetermined length of time has elapsed, a considerableamount of particles is discharged to the outside of the chamber 65, butsome particles are deposited again on the bottom portion of the chamber65. Then, the controller 10 determines whether or not the turn-on of theflash lamps 69 has been performed a predetermined number of times (instep S25). For example, 50 times to 100 times is adopted as thepredetermined number of times. When the number of times the turn-on ofthe flash lamps 69 is performed is less than the predetermined number oftimes, the process returns to step S23 in which the flash lamps 69 areturned on again. The emission of flashes of light by the turn-on of theflash lamps 69 causes the particles deposited again to rise and scatter,and the stream of nitrogen gas carries the particles to the outside ofthe chamber 65. When the number of times the turn-on of the flash lamps69 is performed has reached the predetermined number of times, thecleaning process is terminated.

Referring to FIG. 5 again, after the cleaning process for cleaning theinterior of the chamber 65 is completed, the process proceeds to stepS130 in which an air particle concentration is measured. Prior to themeasurement of the air particle concentration, the open-close valve 95is opened so that the gas existing in the chamber 65 is introduced intothe measurement chamber of the measurement part 50. Then, themeasurement part 50 measures, from a particle concentration of particleshaving particle diameters not less than the predetermined size (particlediameter) and a particle concentration of particles having particlediameters less than the predetermined size (particle diameter), at leastthe particle concentration of particles having particle diameters lessthan the predetermined size. Then, the measurement part 50 supplies aresult of the measurement to the controller 10.

Then, in step S140, the controller 10 determines whether or not theparticle concentration of particles having particle diameters less thanthe predetermined size is equal to or lower than a predeterminedreference value. When, as a result of the determination, the particleconcentration is higher than the reference value, the process returns tostep S120, in which the cleaning of the interior of the chamber 65 isperformed again. When, as a result of the determination, the particleconcentration is equal to or lower than the reference value, the processproceeds to step S150, in which cleaning of the interior of the chamber65 is newly performed. This new cleaning process is performed under astate where a transport operation of the transport robot, an open/closeoperation of the gate valve 68 are performed as if a substrate wastransported into the chamber 65. During the process, the turn-on of theflash lamps 69 is, for example, repeated 25 times to 50 times atintervals of one minute. Except for these different points, the cleaningprocess performed in step S150 is the same as the process performed instep S120. As a result of this cleaning process, particles existing inthe chamber 65 and having particle diameters not less than thepredetermined size (particle diameter), for example, having particlediameters not less than 0.8 um, are mainly removed. That is, in theprocess of step S150, particles having particle diameters larger thanthe particle diameters of the particles mainly removed in the cleaningof step S120 are mainly removed.

After the cleaning process for cleaning the interior of the chamber 65is completed in step S150, the process proceeds to step S160, in whichthe open-close valve 95 is opened so that an air particle concentrationis measured in the same manner as in the measurement in step S130.However, in the measurement in step S160, the measurement part 50measures both of a particle concentration of particles having particlediameters not less than the predetermined size (particle diameter) and aparticle concentration of particles having particle diameters less thanthe predetermined size (particle diameter). Then, the measurement part50 supplies a result of the measurement to the controller 10.

Then, in step S170 of FIG. 6, the controller 10 determines whether ornot the supplied particle concentration of particles having particlediameters not less than the predetermined size is equal to or lower thana predetermined reference value. When, as a result of the determination,the particle concentration is higher than the reference value, theprocess returns to step S150, in which the cleaning of the interior ofthe chamber 65 is performed again. When, as a result of thedetermination, the particle concentration is equal to or lower than thereference value, the process proceeds to step S180, in which thecontroller 10 determines whether or not the particle concentration ofparticles having particle diameters less than the predetermined size isequal to or lower than the reference value. When, as a result of thedetermination, the particle concentration is higher than the referencevalue, the process returns to step S120, in which the cleaning of theinterior of the chamber 65 is performed again. When, as a result of thedetermination, the particle concentration is equal to or lower than thereference value, a particle test of step S190 is conducted. In theparticle test, as already described, a dummy wafer is actually receivedin the chamber 65 and subjected to the same heat treatment as the heattreatment performed on the objective semiconductor wafer W to beprocessed. Then, the dummy wafer is taken out of the chamber 65, andthen transported into a measurement machine that is separately provided.Thereby, the number of particles attached onto the substrate is actuallymeasured. This measurement is performed for both of particles havingparticle diameters not less than the predetermined size, for example,not less than 0.8 um, and particles having particle diameters less thanthe predetermined size.

After the number of particles existing on the substrate is measured,then in step S200, whether or not the number of particles havingparticle diameters less than the predetermined size is equal to orsmaller than a reference value is determined. The reference value is,for example, ten. When, as a result of the determination, the number ofthe particles larger than the reference value, the process returns tostep S120, in which the cleaning of the interior of the chamber 65 isperformed again. When, as a result of the determination, the number ofthe particle is not larger than the reference value, the determinationof step S210 is made to determine whether or not the number of particleshaving particle diameters not less than the predetermined size is equalto or smaller than a reference value. The reference value is, forexample, twenty. When, as a result of the determination, the number ofthe particles is larger than the reference value, the process returns tostep S150, in which the cleaning of the interior of the chamber 65 isperformed again. When, as a result of the determination, the number ofthe particles is equal to or smaller than the reference value, thestart-up process that follows the maintenance of the heat treatmentapparatus is terminated.

After the start-up process that follows the maintenance of the heattreatment apparatus is completed, the semiconductor wafer W isheat-treated. An objective semiconductor wafer W to be heat-treated inthe heat treatment apparatus is a semiconductor wafer implanted withions.

In a heat treatment step, with the susceptor 73 and the heating plate 74situated in the wafer transport position shown in FIG. 1, the transportrobot (not shown) transports the semiconductor wafer W through theopening 66 into the chamber 65, and places the semiconductor wafer Wonto the support pins 70. After the semiconductor wafer W is received inthe chamber 65, the opening 66 is closed by the gate valve 68.Thereafter, the susceptor 73 and the heating plate 74 are driven by themotor 40 to move upward to the wafer heat treatment position shown inFIG. 2, thereby holding the semiconductor wafer W in a horizontalattitude. The open-close valves 80, 81 and 85 are opened to produce thestream of nitrogen gas in the chamber 65.

The susceptor 73 and the heating plate 74 are heated in advance to apredetermined temperature under the action of the heater incorporated inthe heating plate 74. Thus, in a state where the susceptor 73 and theheating plate 74 are moved upward to the wafer heat treatment position,the semiconductor wafer W is preheated by contacting the susceptor 73that is heated. Thus, the temperature of the semiconductor wafer W risesgradually.

In this state, the semiconductor wafer W is heated through the susceptor73 without interruption. During the temperature rise of thesemiconductor wafer W, a temperature sensor (not shown) always monitorswhether or not the surface temperature of the semiconductor wafer W hasreached a preheating temperature T1.

The preheating temperature T1 ranges, for example, from about 200° C. toabout 600° C. Heating the semiconductor wafer W to the preheatingtemperature T1 within such a range does not diffuse the ions implantedin the semiconductor wafer W.

When the surface temperature of the semiconductor wafer W reaches thepreheating temperature T1, the flash lamps 69 are turned on to performflash heating. A length of time during which the flash lamps 69 are ONin the flash heating step ranges from about 0.1 millisecond to about 10milliseconds. The flash lamps 69 emit extremely intense flashes of lightbecause previously stored electrostatic energy is converted into such anultrashort light pulse.

Such flash heating causes the surface temperature of the semiconductorwafer W to instantaneously reach a temperature T2. The temperature T2 isa temperature ranging from about 1000° C. to about 1100° C. and requiredfor a process of activating the ions in the semiconductor wafer W. Thetemperature rise of the surface of the semiconductor wafer W to thistreatment temperature T2 activates the ions implanted in thesemiconductor wafer W.

In this process, the activation of the ions in the semiconductor wafer Wis completed in a short time because the surface temperature of thesemiconductor wafer W is raised to the treatment temperature T2 in anextremely short time ranging from about 0.1 millisecond to 10milliseconds. This causes no diffusion of the ions implanted in thesemiconductor wafer W, and therefore can prevent occurrence of aphenomenon in which the ions implanted in the semiconductor wafer Wexhibit a round or dull profile. Because a length of time required forthe activation of ions is much shorter than a length of time requiredfor the diffusion of the ions, the activation of the ions is completedeven in a short time ranging from about 0.1 millisecond to about 10milliseconds which causes no diffusion.

Additionally, before the flash lamps 69 are turned on to heat thesemiconductor wafer W, the surface temperature of the semiconductorwafer W is raised up to the preheating temperature T1 ranging from about200° C. to about 600° C. by using of the heating plate 74. This enablesthe temperature of the semiconductor wafer W to be rapidly raised up tothe treatment temperature T2 ranging from about 1000° C. to about 1100°C. by the flash lamps 69.

After the flash heating step, the susceptor 73 and the heating plate 74are driven by the motor 40 to move downward to the wafer transportposition shown in FIG. 1, and the opening 66 having been closed by thegate valve 68 is opened. The transport robot (not shown) transports thesemiconductor wafer W placed on the support pins 70 out of the chamber65. In the above-mentioned manner, a series of heat treatment operationsis completed.

In the heat treatment apparatus according to this preferred embodimenthaving the above-described configuration, the air particle concentrationin the processing space of the chamber 65 is measured by the measurementpart 50. The air particle concentration is correlated with the number ofparticles attached to the substrate that is received in the processchamber. Therefore, by conducting the particle test after the airparticle concentration in the processing space is lowered to an airparticle concentration corresponding to the number of particles existingon a substrate which can pass the particle test, the number of times theparticle test should be conducted after the maintenance of the heattreatment apparatus can be reduced. Additionally, since the measurementpart 50 is provided in the apparatus itself, time and effort requiredfor measurement of the air particle concentration are much smaller thanthose required for the particle test. Accordingly, the heat treatmentapparatus according to this preferred embodiment can achieve aconsiderable cost reduction.

Moreover, in the heat treatment apparatus according to this preferredembodiment having the above-described configuration, the correlationinformation indicating the correlation between the air particleconcentration in the processing space of the chamber 65 and the numberof particles attached to the substrate received in the chamber 65 isstored in the magnetic disk 14. Based on a result of the measurement bythe measurement part 50 and the correlation information, the controller10 calculates the number of particles that will be attached to asubstrate intended to be received in the chamber 65. The particle testis conducted only when the particle concentration in the processingspace is equal to or lower than the reference value, that is, only whena result of the calculation of the number of particles attached to thesubstrate is equal to or less than a predetermined specified value.Accordingly, even though the particle test actually using a substrate isnot conducted, the particle concentration in the chamber 65 can belowered to a level at which the particle test can be passed.

Furthermore, in the heat treatment apparatus according to this preferredembodiment having the above-described configuration, the outlet passage93 that exhausts the measurement part 50 is provided. This can moresmoothly introduce the gas existing in the chamber 65 into themeasurement chamber of the measurement part 50.

Furthermore, in the heat treatment apparatus according to this preferredembodiment having the above-described configuration, the inside diameterof the outlet passage 93 that exhausts the measurement part 50 issmaller than the inside diameters of the outlet passages 79 and 84 thatexhaust the interior of the chamber 65. Accordingly, a back flow of thegas from the outlet passage 93 toward the measurement part 50 is notlikely to occur. Thus, the accuracy of measurement of the air particleconcentration is further improved.

Furthermore, in the heat treatment apparatus according to this preferredembodiment having the above-described configuration, the flash lamps 69are provided, and the flash lamps 69 emit a light flash to the substratereceived in the chamber 65 to thereby heat-treat the received substrate.In a case of adopting a light flash of flash lamps, a large impact isgiven to the substrate during the heat treatment and therefore crackingof the substrate is likely to occur. As a result, the frequency of themaintenance increases. However, in the heat treatment apparatusaccording to this preferred embodiment, the measurement part 50 measuresthe air particle concentration. This makes it easy to examine a resultof the cleaning performed in the start-up process that follows themaintenance. Accordingly, even if the frequency of the maintenanceincreases due to the emission of flashes of light, a cost increase inthe start-up process can be suppressed as compared with a case of notusing the air particle concentration.

Furthermore, in the heat treatment apparatus according to this preferredembodiment having the above-described configuration, air particles inthe processing space of the chamber 65 are removed by using acombination of the light source 5 including the flash lamps 69 and thelike with the supply and exhaust system. This enables the air particleconcentration in the processing space of the chamber 65 to be lowered toa level at which the particle test can be passed.

Second Preferred Embodiment

Next, a second preferred embodiment of the present invention will bedescribed. A configuration of a heat treatment apparatus according tothe second preferred embodiment is completely the same as that of thefirst preferred embodiment. In the first preferred embodiment, after themaintenance operation, the air particle concentration is measured andthe cleaning process for cleaning the chamber 65 is performed. In thesecond preferred embodiment, on the other hand, the air particleconcentration is measured during the heat treatment being performed onthe semiconductor wafer W, and a cleaning process as needed isperformed. Specifically, in the heat treatment apparatus according tothe present invention, the measurement part 50 that measures an airparticle concentration is attached to the chamber 65, to enable the airparticle concentration in the chamber 65 to be measured as needed evenduring a process being performed on the semiconductor wafer W.Therefore, in the second preferred embodiment, the air particleconcentration in the chamber 65 is measured during a steady processbeing performed on the semiconductor wafer W, and particle removalprocess in accordance with an obtained concentration level is performed.

FIG. 8 is a flowchart showing a process in the heat treatment apparatusaccording to the second preferred embodiment. Firstly, the air particleconcentration is measured during a process being performed on thesemiconductor wafer W (step S30). Details of the heat treatmentperformed on the semiconductor wafer W in the heat treatment apparatusare as described in the first preferred embodiment. That is, the flashheating is performed using the flash lamps 69 emitting a light flash tothe surface of the semiconductor wafer W that has been held in thechamber 65 and preheated by the heating plate 74 and the susceptor 73.

At any timing during such a steady heat treatment being performed on thesemiconductor wafer W, the measurement part 50 measures the air particleconcentration in the processing space of the chamber 65. The particlesize (particle diameter) for which the measurement part 50 performs themeasurement during the process can be set to any appropriate value. Aresult of the measurement by the measurement part 50 is transmitted tothe controller 10.

In the second preferred embodiment, three levels of threshold values areset for the air particle concentration during the wafer process, andprocessing in accordance with the concentration level is performed. Tobe specific, when the air particle concentration during the waferprocess exceeds a level 3 (third threshold value), a process shown in aflowchart of FIG. 9 is performed (step S40). When the air particleconcentration is equal to or lower than the level 3 and exceeds a level2 (second threshold value), a process shown in a flowchart of FIG. 10 isperformed (step S50). When the air particle concentration is equal to orlower than the level 2 and exceeds a level 1 (first threshold value), aprocess shown in a flowchart of FIG. 11 is performed (step S60).

Here, the level 1, which is the first threshold value for determiningthe air particle concentration, indicates an air particle concentrationcorresponding to a situation where the number of particles attached toone wafer increases by 25 to 50 when comparing before and after theheat-treatment of the semiconductor wafer W in the heat treatmentapparatus. The level 2, which is the second threshold value formeasuring the air particle concentration, is an air particleconcentration corresponding to a situation where the number of particlesattached to one wafer increases by 51 to 100 when comparing before andafter the heat treatment of the semiconductor wafer W. The level 3,which is the third threshold value for measuring the air particleconcentration, is an air particle concentration corresponding to asituation where the number of particles attached to one wafer increasesby 101 or more when comparing before and after the heat treatment of thesemiconductor wafer W.

FIG. 12 shows the correlation between the increment of the number ofparticles existing on the semiconductor wafer W and the air particleconcentration before and after the process. The meaning of FIG. 12 issimilar to the meaning of FIG. 4. The increment of the number ofparticles existing on the wafer is generally proportional to the airparticle concentration. The level 3, which corresponds to a situationwhere the increment of the number of particles is large, is higher thanthe level 2, and the level 2 is higher than the level 1. Based on aresult of the measurement by the measurement part 50, the controller 10determines which of the levels the air particle concentration in thewafer process is found at. Then, for example, the controller 10 causesthe result of the determination to be displayed on the display part 21(FIG. 3). Then, based on contents thus displayed, processing inaccordance with the level of the air particle concentration isperformed.

For convenience of the description, procedures taken when it isdetermined in step S60 that the air particle concentration is equal toor lower than the level 2 and exceeds the level 1 will be described inthe first place. FIG. 11 is a flowchart showing procedures taken whenthe air particle concentration exceeds the level 1. A situation wherethe air particle concentration is equal to or lower than the level 2 andexceeds the level 1 is a situation where minor contamination withparticles occurs in the chamber 65. When such minor contaminationoccurs, the particles existing in the chamber 65 are removed with amaximum flow rate of the supply and exhaust to and out of the chamber65. Hereinafter, a specific description will be given to the procedurestherefore.

Firstly, when it is determined that the air particle concentration isequal to or lower than the level 2 and exceeds the level 1, the processof the semiconductor wafer W is interrupted (step S61). Here, theprocess of the semiconductor wafer W being treated in the heat treatmentapparatus is not immediately interrupted, but the process is interruptedat a good timing which comes when a certain section of the process iscompleted. For example, the process is interrupted after the treatmentof the final semiconductor wafer W of a lot including the currentlytreated semiconductor wafer W is completed.

After the wafer process is interrupted, supply and exhaust to and out ofthe chamber 65 are performed with the highest flow rate for 30 seconds(step S62). To be specific, by means of the mass flow controller 89provided in the gas pipe 82, the flow rate of the nitrogen gas suppliedto the chamber 65 is set to be the highest flow rate (for example,corresponding to 50 liters/min). At the same time, an exhaust path forexhausting the chamber 65 is switched to the large-diameter pipe of theexhaust pipe 83, and the chamber 65 is exhausted with the highest flowrate.

After such supply and exhaust to and out of the chamber 65 with thehighest flow rate are performed for 30 seconds, supply and exhaust toand out of the chamber 65 with a normal flow rate are performed for 15seconds (step S63). More specifically, by means of the mass flowcontroller 89, the flow rate of the nitrogen gas supplied to the chamber65 is set to be the flow rate (for example, 20 liters/min) adopted in anormal wafer process, and the exhaust path is switched to thesmall-diameter pipe of the exhaust pipe 83. Thus, the chamber 65 isexhausted with the normal flow rate.

The supply and exhaust (30 seconds) with the highest flow rate in stepS62 and the supply and exhaust (15 seconds) with the normal flow rate instep S63 are repeated 50 times (step S64). Repeating the supply andexhaust with the highest flow rate and the supply and exhaust with thenormal flow rate in this manner allows the particles remaining in thechamber 65 to be discharged to the outside of the chamber 65. A lengthof time of the supply and exhaust with the highest flow rate, a lengthof time of the supply and exhaust with the normal flow rate, and thenumber of times they are repeated, are merely illustrative, and theirvalues are not limited to the illustrated ones.

Then, the measurement part 50 measures the air particle concentration inthe chamber 65 (step S65). When a result of the measurement by themeasurement part 50 indicates that the air particle concentration isequal to or lower than the above-mentioned level 1, the process proceedsfrom step S66 to step S58, in which the process of the semiconductorwafer W in the heat treatment apparatus is restarted.

On the other hand, when the air particle concentration still exceeds thelevel 1 even after particles are removed by the repetition of the supplyand exhaust with the highest flow rate and the supply and exhaust withthe normal flow rate, the process of steps S62 to S64 is additionallyrepeated twice (step S67). That is, a process in which the supply andexhaust with the highest flow rate and the supply and exhaust with thenormal flow rate are repeated 50 times is performed twice. It should benoted that the number of times of the repetition in step S67 is notlimited to twice, and it may be once or three times.

Then, the measurement part 50 measures the air particle concentration inthe chamber 65 again (step S68). When, as a result of there-measurement, the air particle concentration is equal to or lower thanthe level 1, the process proceeds from step S69 to step S58, in whichthe process of the semiconductor wafer W in the heat treatment apparatusis restarted. On the other hand, when the air particle concentrationstill exceeds the level 1, a particle removal process corresponding tothe level 2 is performed, as follows.

FIG. 10 is a flowchart showing procedures taken when the air particleconcentration exceeds the level 2 in step S50 of FIG. 8. A situationwhere the air particle concentration is equal to or lower than the level3 and exceeds the level 2 is a situation where a medium degree ofcontamination with particles occurs in the chamber 65. When such amedium degree of contamination occurs, “ghost run” is carried out toremove particles existing in the chamber 65.

Firstly, when it is determined that the air particle concentration isequal to or lower than the level 3 and exceeds the level 2, the processof the semiconductor wafer W is immediately interrupted (step S51). Morespecifically, the semiconductor wafer W that is currently processed iscontinued to be processed, but transport of any new semiconductor waferW into the heat treatment apparatus is stopped. When the contaminationin the chamber 65 is minor (when the air particle concentration is equalto or lower than the level 2 and exceeds the level 1), the continuationof the process is barely allowed. However, when the contamination is atthe medium degree (when the air particle concentration is equal to orlower than the level 3 and exceeds the level 2), the continuation of theprocess involves a high risk of producing a fault wafer. Therefore, theprocess is immediately interrupted.

After the wafer process is immediately interrupted, the ghost run iscarried out 100 times (step S52). Also when it is determined in step S69of FIG. 11 that the air particle concentration exceeds the level 1, theprocess proceeds to step S52, in which the ghost run is carried out 100times. Here, the “ghost run” means a process in which the flash lamps 69are turned on under a nitrogen atmosphere while the transport robot, thegate valve 68, the heating plate 74, and the like, are operated as if awafer was transported into the chamber 65. The “ghost run” is the sameprocess as the process performed in step S150 of FIG. 5. To be specific,although there is actually no semiconductor wafer W, a semiconductorwafer W is imaginarily transported and the imaginary semiconductor waferW is processed to discharge particles from the chamber 65. Carrying outsuch ghost run 100 times allows particles remaining in the chamber 65 tobe removed. The number of times the ghost run is carried out is notlimited to 100 times, and it may be any appropriate number of times.

Then, the measurement part 50 measures the air particle concentration inthe chamber 65 (step S53). When a result of the measurement by themeasurement part 50 indicates that the air particle concentration isequal to or lower than the above-mentioned level 1, the process proceedsfrom step S54 to step S58, in which the process of the semiconductorwafer W in the heat treatment apparatus is restarted.

On the other hand, when the air particle concentration still exceeds thelevel 1 even after particles are removed by the ghost run, the ghost runis carried out 100 times again (step S55). The number of times the ghostrun is carried out in step S55 is also not limited to 100 times, and itmay be any appropriate number of times.

Then, the measurement part 50 measures the air particle concentration inthe chamber 65 again (step S56). When, as a result of there-measurement, the air particle concentration is equal to or lower thanthe level 1, the process proceeds from step S57 to step S58, in whichthe process of the semiconductor wafer W in the heat treatment apparatusis restarted. On the other hand, when the air particle concentrationstill exceeds the level 1, a particle removal process corresponding tothe level 3 is performed, as follows.

FIG. 9 is a flowchart showing procedures taken when the air particleconcentration exceeds the level 3 in step S40 of FIG. 8. A situationwhere the air particle concentration exceeds the level 3 is a situationwhere major contamination with particles occurs in the chamber 65. Whensuch major contamination occurs, it is necessary to open the chamber 65and carry out the maintenance. Here, in some cases, when the airparticle concentration is measured during the wafer process in step S30of FIG. 8, the air particle concentration suddenly exceeds the level 2or the level 3. One conceivable reason therefore is that thesemiconductor wafer W brings particles into the chamber 65 or a troubleoccurs in the gas supply and exhaust system for supplying and exhaustinga gas to and out of the chamber 65.

When it is determined that the air particle concentration exceeds thelevel 3, the process of the semiconductor wafer W is immediatelyinterrupted (step S41). This is the same as the immediate interruptionshown in FIG. 10. That is, the semiconductor wafer W that is currentlyprocessed is continued to be processed, but transport of any newsemiconductor wafer W into the heat treatment apparatus is stopped. Thecontamination in the chamber 65 is major (when the air particleconcentration exceeds the level 3), the continuation of the processinvolves an extremely high risk of producing a fault wafer. Therefore,the process is immediately interrupted.

After the wafer process is immediately interrupted, the chamber 65 isopened and the maintenance is carried out (step S42). Also when it isdetermined in step S57 of FIG. 10 that the air particle concentrationexceeds the level 1, the process proceeds to step S42, in which themaintenance is carried out. This maintenance step is the same as stepS110 of FIG. 5. After the maintenance, a process that follows themaintenance is performed (step S43). The process that follows themaintenance is the same as that performed in steps S120 to S210 of thefirst preferred embodiment shown in FIGS. 5 and 6. That is, inconsideration of a result of the measurement of the air particleconcentration by the measurement part 50, an actual particle test isconducted.

In this manner, in the second preferred embodiment, the measurement part50 measures the air particle concentration during the heat treatmentbeing performed on the semiconductor wafer W, and a particle removal inaccordance with the concentration level is performed. In the heattreatment apparatus according to the present invention, the measurementpart 50 that measures an air particle concentration is attached to thechamber 65, to enable the air particle concentration in the chamber 65to be measured as needed even during a process being performed on thesemiconductor wafer W. When the particle concentration obtained as aresult of the measurement exceeds the predetermined threshold value,particles existing in the chamber 65 are removed. Accordingly, even whenthe particle concentration in the chamber 65 increases during theprocess of the semiconductor wafer W, the number of particles can bepromptly reduced.

When the air particle concentration obtained as a result of themeasurement during the wafer process is equal to or lower than the level3 (when a status of contamination in the chamber 65 is at a minor ormedium degree), the particle removal process is performed withoutopening the chamber 65. This can reduce a downtime of the heat treatmentapparatus.

<Modifications>

While the present invention has been shown and described in detail, theforegoing description is in all aspects illustrative and notrestrictive. Therefore, in the preferred embodiments of the presentinvention, modifications and omissions can be appropriately given withinthe scope of the invention. For example, the usefulness of the presentinvention is not impaired even when the present invention directed tothe measurement of an air particle concentration is applied to anapparatus, such as an RTP apparatus or a single-wafer type CVDapparatus, that performs the heat treatment using something other thanflash lamps. Moreover, although the heat treatment apparatus accordingto this preferred embodiment preheats a substrate by means of a heatingplate at a time of the heat treatment, the preheating may be performedby using heat radiated from halogen lamps or the like.

In the first preferred embodiment, it may be acceptable that a wafer istransported about 50 times in a time period between step S150 and stepS160. At this time, a dummy wafer is transported in accordance with anormal process flow, and received in the chamber 65. As for the flashheating, for example, the flash heating is performed in 25-timestransports among the 50-times transports, and not performed in theremaining 25-times transports. Transporting the dummy wafer into and outof the chamber 65 causes particles remaining in the chamber 65 to beattached to the dummy wafer and thus brought out. As a result, theparticle removal effect is further enhanced. In performing the particleremoval by means of such wafer transports, it is preferable to use a newdummy wafer each time.

Furthermore, after the ghost run is performed in the second preferredembodiment (after step S52 and step S55), too, the wafer transport maybe carried out about 50 times to enhance the particle removal effect.

While the invention has been described in detail, the foregoingdescription is in all aspects illustrative and not restrictive. It isunderstood that numerous other modifications and variations can bedevised without departing from the scope of the invention.

What is claimed is:
 1. A cleaning method for cleaning inside of aprocess chamber of a heat treatment apparatus for heating a substrate,comprising the steps of: (a) discharging particles scattered by flashesof light emitted from a flash lamp toward an interior of said processchamber to outside of said process chamber by a stream of gas whilepreventing a substrate from being transported into said process chamber;and (b) introducing a gas in a processing space provided in said processchamber into a measurement part and measuring an air particleconcentration in the gas, and in a case where said air particleconcentration measured in said gas is higher than a reference value,returning to said step (a).
 2. The cleaning method according to claim 1,wherein said step (a) includes the step of: (a-1) emitting flashes oflight from said flash lamp without performing an operation of a drivingmechanism in said process chamber; and said step (b) includes the stepof: (b-1) in a case where an air particle concentration of particleshaving diameters less than a predetermined size is higher than areference value, returning to said step (a-1).
 3. The cleaning methodaccording to claim 2, wherein said step (a) further includes the stepof: (a-2) emitting flashes of light from said flash lamp whileperforming an operation of said driving mechanism in said processchamber; and said step (b) further includes the step of: (b-2) in a casewhere an air particle concentration of particles having diameters notless than said predetermined size is higher than a reference value,returning to said step (a-2).